Kurds are refusing to accept the authority of the new provincial governor, the head of an Arab nationalist party that opposes Kurdish aspirations to join part of Nineveh with Iraqi Kurdistan.

BASHIQA, IRAQ — On a quiet stretch of road flanked by the rolling hills of northern Nineveh province stands a checkpoint many fear could become the next frontline in a new conflict over age-old issues of land and power dividing Arabs and Kurds.

To the west lies the provincial capital, Mosul: insurgent-infested and, since April, governed by a hard-line Arab nationalist group that is seeking to affirm Nineveh's Arab identity.

To the east lies a string of mostly Kurdish, mostly calm towns and villages that nominally are part of Nineveh but that have been controlled by Kurdish-speaking peshmerga forces since the U.S.-led invasion of Iraq in 2003.

Fresh tension in the area comes from the Kurds' refusal to accept the authority of the region's new Arab governor, Atheel Najafi, unless they gain positions in Mosul's city council, currently controlled by Najafi's Hadba coalition.

When Najafi tried to visit Bashiqa last month, protesters armed with eggs and tomatoes thronged the road to block his path, and peshmerga guards at the checkpoint telephoned Iraqi security forces in Mosul to warn the governor to stay away.

Najafi says he will not negotiate unless the Kurdish militia withdraws from Nineveh territory and allows the Iraqi army to take control. He also vowed to return Arabs to the area, which Kurds reclaimed after the fall of Saddam Hussein's Arab nationalist regime.

The dispute mixes constitutional issues with ancient feuds over ethnicity, land and resources. As U.S. forces prepare to scale back in Iraq, the potential for trouble is real, said Joost Hiltermann of the Brussels-based International Crisis Group.

"It's very serious," he said. "Both sides have dug in and the only thing preventing open conflict is the Americans, who have been trying to mediate and prevent both sides using military force."

The U.S. military takes no position on the Kurdish-Arab dispute but is eager to persuade the two sides to talk through their problems while American forces are still around, said Brig. Gen. Robert Brown, the U.S. commander in Nineveh.

Brown sees a wild card in the militant group Al Qaeda in Iraq, which maintains a stubbornly resilient presence in Mosul.

"Al Qaeda is always trying to spark tensions, and as they did with Sunnis and Shiites, they're doing it with Arabs and Kurds," he said.

Kurds had dominated Nineveh's provincial council before the elections in January, because Sunnis had boycotted the January 2005 vote. But now Kurds worry about their future as a minority group in Iraq.

Hassan Narmo, mayor of Shaikhan, one of the 15 Nineveh towns and districts refusing to acknowledge the authority of the Hadba administration, described the Arab party as "a very hard-line group."

"We think they're practicing the same policies as the former regime," Narmo said. "They want to monopolize power and that took Iraq to the abyss before."

The Kurdish objection to Arab authority touches on issues other than the composition of a provincial council. At stake is the identity of Iraq's young democracy, and whether it will continue to be built on the principle of consensus that defined the formation of the first post-invasion governments, or whether it will evolve into a majority-rule form of governance.

The Kurds say Najafi's refusal to give them positions on the council violates the spirit of consensus in which the constitution was written.

Prime Minister Nouri Maliki has espoused positions similar to Najafi's, emphasizing his desire to extend army control across all Iraqi territory and also expressing a preference for majority rule. But he can't afford to alienate the Kurds, allies in his coalition government in Baghdad.

"We are worried he is playing a double-faced game, and this is very dangerous in Iraq," said Sadi Pire, a senior official with one of the main Kurdish factions in Iraqi Kurdistan, reflecting widely held Kurdish suspicions about Maliki's position.

Further complicating the issue are Kurdish aspirations to have the region join the semiautonomous region of Iraqi Kurdistan. With national elections scheduled for January, it's unlikely politicians will reach a compromise in the coming months, Hiltermann said, and the dispute could fester into next year and remain unresolved by August 2010, when the U.S. military is scheduled to withdraw its combat troops.

Some Kurds feel irked by the U.S. neutrality, which they regard as a betrayal after Kurdish support during the initial stages of the U.S.-led invasion. They fear that once U.S. forces withdraw, Kurds will find themselves without allies in a region traditionally hostile to their national aspirations.

"The U.S. withdrawal will definitely make things worse," said Narmo, the Shaikhan mayor, "because nothing in Iraq is solved."